.app { height: 100vh; padding-top: 100px; }

.row { display: flex; align-items: center; justify-content: center; margin-bottom: 16px; }
.button {
  font-size: 32px;
  padding: 4px 12px;
  border: 2px solid transparent;
  color: rgb(112, 76, 182);
  cursor: pointer;
  background-color: rgba(112, 76, 182, 0.1);
  border-radius: 10px;
  transition: all 0.15s;
}

.button:hover,
.button:focus  { border: 2px solid rgba(112, 76, 182, 0.4); }
.button:active { background-color: rgba(112, 76, 182, 0.2); }

.value { font-size: 78px; padding: 0 16px; font-family: 'Courier New', Courier, monospace; }

.textbox {
  font-size: 32px;
  padding: 4px;
  width: 64px;
  text-align: center;
  margin-right: 8px;
  border-radius: 10px;
}

.asyncButton { position: relative; margin: 0 8px; overflow: hidden; }
.asyncButton:after {
  content: '';
  display: block;
  width: 100%;
  height: 100%;
  background-color: rgba(112, 76, 182, 0.15);
  position: absolute;
  left: 0;
  top: 0;
  opacity: 0;
  transition: width 1s linear, opacity 0.5s ease 1s;
}
.asyncButton:active:after { width: 0%; opacity: 1; transition: 0s; }